The classic question of how to beat low teirs as marth

[Brave]

Hi guys! i'm Brave and i'm a marth main from florida. so every marth main knows the matchup vs fox including myself. my problem has recently been that there are a few low teir mains that i just cant seem to get around. for one there is a donkey kong player down here who i have trouble with. granted he is better than me but i cant seem to do anything to his donkey kong and i know part of the reason im losing is because i don't know the matchup.
some of my dk problems are...

- where do i throw him off of a grab? i dont seem to get much off of one
- what is the best way to approach donkey kong? i feel like the best think i can do is like d tilt
- how do i legegaurd dk? ive tried alot of stuff but it seems like im not doing it quite right
- lastly where do i want to put dk? am i trying to juggle him? combo him off the side? idk

now there is another low teir i have problems with and that is mewtwo. i actuily have a match that i can link for this one (although i didnt play particularly well)

-mewtwo seems like he loved to w/d oos grab how do i deal with this?
-what is the best way to ledgegaurd mewtwo?
-and where do i combo mewtwo? should i be trying to go for fair->fsmash or should i just be looking for stray hits
sorry for this incredibly long post but if someone can help me i would greatly appreciate it.